Search

Abstract: In temperate areas, dormancy (diapause and/or quiescence) enables herbivorous insect species to persist and thrive by synchronizing growth and reproduction with the seasonal phenology of their host plants. Within-population variability in dormancy increases survival chances under unpredictable environmental changes. However, prolonged dormancy may be costly, incurring trade-offs in important adult fitness traits such as life span and reproduction. We used the European cherry fruit fly, Rhagoletis cerasi, a stenophagous, univoltine species that overwinters in the pupal stage for usually one or more years to test the hypotheses that prolonged dormancy of pupae has trade-offs with body size, survival and reproduction of the resulting adults. We used two geographically isolated populations of R. cerasi to compare the demographic traits of adults obtained from pupae subjected to one or two cycles of warm–cold periods (annual and prolonged dormancy respectively). Regardless of population, adults from pupae that experienced prolonged dormancy were larger than counterparts emerging within 1year. Prolonged dormancy did not affect adult longevity but both lifetime fecundity and oviposition were significantly decreased. Extension of the life cycle of some individuals in R. cerasi populations in association with prolonged dormancy is likely a bet-hedging strategy. [Copyright &y& Elsevier]

Abstract: Osmia (Osmia) bees are strictly univoltine and winter as diapausing adults. In these species, the timing of adult eclosion with the onset of wintering conditions is critical, because adults exposed to long pre-wintering periods show increased lipid loss and winter mortality. Populations from warm areas fly in February–March and are exposed to longer growth seasons than populations from colder areas, which fly in April–May. Given their inability to produce an extra generation, early-flying populations should develop more slowly than late-flying populations and thus avoid the negative consequences of long pre-wintering periods. In this study we compare the development under natural and laboratory conditions of phenologically-distinct populations in two Osmia species. Early-flying populations took ∼2months longer to develop than late-flying populations. Differences between populations in larval and pupal period duration were very small, whereas the prepupal period was much longer in early-flying populations. In contrast to the larval and pupal stages, the prepupal stage showed a non-linear response to temperature, was strongly affected by thermoperiod, and exhibited minimum respiration rates. Coupled with other lines of evidence, these results suggest that the prepupal period in Osmia corresponds to a summer diapause, and its duration may be under local selection to synchronize adult eclosion with the onset of winter temperatures. We discuss the implications of our results relative to current expectations of global warming. [Copyright &y& Elsevier]

Abstract: Food has an influence on many life history traits related to dormancy in insects. In our previous study with the rice bug Leptocorisa chinensis (Dallas) (Hemiptera: Alydidae), diapausing females transferred to conditions physically favorable for promoting the gonad development required food intake to resume gonad development, whereas males did not. These differences in response to food between males and females lead to two questions: (1) Was diapause in the starved females completed? (2) Were the starved males that resumed gonad development at the same physiological status as fed males? We tested these questions with two physiological indicators: gonad status and respiratory rate. Results indicate that starved females are able to complete diapause, but show depressed respiration relative to well-fed insects in diapause. Similar to females, starved males that resumed postdiapause gonad development also had depressed respiratory rate, and hence physiological status is presumed to be different between starved and fed individuals. In this study, it was also found that the photoperiodic signal is storable, whereas the food signal acts directly. The adaptive significance of regulation of gonad development and respiratory metabolism in relation to phenology of suitable host plant and reproductive strategy is discussed in both sexes. [Copyright &y& Elsevier]

Abstract: We investigated the mode of action of winter cold in the termination of diapause by investigating Time-Interval-Measuring Enzyme (TIME). First, we determined the period of cold required for the completion of diapause development. Synchronously developing egg batches of a pure strain (C108 Bombyx mori silkworm) were used to minimize variations in hatching time. Hatching occurred with only 18 days chilling at 5°C when the incubation at 25°C after the chilling was elongated. The 18-day period was much shorter than we expected; diapause in B. mori is known to terminate completely with about 100 days of chilling. Even in such a short period of chilling, no sporadic hatching occurred. Moreover, we determined that a temperature-insensitive stage, which we called “Neboke”, followed the short cold-requiring stage. Thus, the stage of diapause development was demarcated from other stages of diapause. While the length of diapause development was elongated when chilling was delayed after oviposition, the Neboke stage length was invariant. Cold evidently exerts its effect only on diapause development. When TIME was purified from eggs and chilled in test tubes, a transitory burst of its ATPase activity occurred at a time equivalent to shortly before the completion of diapause development; this was an interval-timer activation. The mechanism by which cold activates TIME to measure the time interval may help explain in biochemical terms the insect''s adaptation to its seasonal environments. [Copyright &y& Elsevier]